Information recording apparatus and information recording method

ABSTRACT

In a recording strategy suitable for high-speed recording, a laser driving signal includes a top pulse having a pulse width corresponding to a recording mark length and multi-pulses having a period 3-times larger than a base clock period of a recording mark. The top pulse is has the first identical-shape top pulses when the recording mark length is 3nT (“n” is a natural number), the second identical-shape top pulses when the recording mark length is (3n+1)T, and the third identical-shape top pulses when the recording mark length is (3n+2)T.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of optically recording information onan information recording medium.

2. Description of the Related Art

Onto a recordable or rewritable optical disc such as a DVD-R(DVD-Recordable) or a DVD-RW (DVD-Rerecordable), information is recordedthereon by irradiating a laser beam on its recording surface. At theareas on the recording surface of the optical disc where the laser beamis irradiated, the property of the optical recording medium forming theoptical disc is physically changed because of the increased temperature.This generates recording marks on the recording surface.

Therefore, if the laser beam is modulated by a pulse waveform (it iscalled “strategy”) corresponding to information to be recorded, andirradiated on the optical disc, recording marks having lengthscorresponding to the information to be recorded can be formed on theoptical disc.

As a strategy for recording the information on a rewritable optical discsuch as a DVD-RW, there is well known a strategy including a top pulseand multi-pulses (they are also called “pulse train”) of the numbercorresponding to recording mark lengths. For instance, an examplethereof is disclosed in Japanese Patent No. 2801510.

Recently, there is a demand of the strategy which is adapted tohigh-speed recording of more than 4-times higher speed, for the purposeof improvement of a recording speed. However, according to the strategywhich utilizes the above-mentioned multi-pulse, ON/OFF switching of thepulse has to be executed within a time of 1T (“T” indicates a base clockperiod of a recording signal) because multi-pulse number is increased in1T unit corresponding to the recording mark length. Therefore, if thebase clock becomes higher speed in the high-speed recording and the timeof 1T becomes shorter, it becomes difficult to obtain an accurateemitting waveform because the rounding portion of the multi-pulsewaveform becomes larger by a transient response. Thus, a recordingcharacteristic of the optical disc is easily affected by differences ofcharacteristics of a laser light source and a driving circuit betweenrecording apparatuses.

Also, since heating by the laser beam and cooling cannot be executedlonger than a 1T time period in the multi-pulse period, the mark cannotbe formed satisfactorily dependently on the characteristic of theoptical disc, and the recording characteristic sometimes becomes worse,like the decrease of a signal modulating degree. The present inventionhas been achieved in order to solve the above problems.

SUMMARY OF THE INVENTION

The present invention has been achieved in order to solve the aboveproblems. It is an object of this invention to provide an informationrecording method and an apparatus thereof which are hardly affected by acharacteristic of the recording apparatus even during a time ofhigh-speed recording, and which can accurately form pits on an opticaldisc by ensuring enough time for heating and cooling.

According to one aspect of the present invention, there is provided aninformation recording apparatus including a signal generating unit whichgenerates a light source driving signal having a top pulse andmulti-pulse of a necessary number corresponding to a recording marklength of recording data, and a recording unit which irradiates arecording light on an optical recording medium by driving a light sourcebased on the light driving signal and forms recording marks on theoptical recording medium, wherein the signal generating unit includes, amulti-pulse generating unit which generates a multi-pulse having aperiod 3-times larger than a base clock period T of the recording mark,and a top pulse generating unit which generates first identical-shapetop pulses when the recording mark length is 3nT (“n” is an integralnumber), and second identical-shape top pulses when the recording marklength is (3n+1)T, and third identical-shape top pulses when therecording mark length is (3n+2)T.

According to another aspect of the present invention, there is providedan information recording method including: a signal generating processwhich generates a light source driving signal having a top pulse andmulti-pulse of a necessary number corresponding to a recording marklength of recording data; and a recording process which irradiates arecording light on an optical recording medium by driving a light sourcebased on the light driving signal, and forms recording marks on theoptical recording medium, wherein the signal generating processincluding: a multi-pulse generating process which generates amulti-pulse having a period 3-times larger than a base clock period T ofthe recording mark; and a top pulse generating process which generatesfirst identical-shape top pulses when the recording mark length is 3nT(“n” is an integral number), and second identical-shape top pulses whenthe recording mark length is (3n+1)T, and third identical-shape toppulses when the recording mark length is (3n+2)T.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a waveform chart showing examples of a strategy and a laserdriving waveform during the time of high-speed recording which utilizesa base clock of 1T period.

FIG. 2A is a graph showing an examined result of a recordable recordingmark length by a combination of one top pulse and cooling pulse, andFIG. 2B is a chart of the waveform.

FIG. 3A is a waveform chart of multi-pulse trains of a plurality ofperiods, and FIG. 3B is a graph showing signal modulating degrees ofrecording marks formed by the waveform.

FIG. 4 is a diagram schematically showing a basic configuration of alaser recording waveform according to the embodiment of the presentinvention.

FIG. 5 is a block diagram showing a schematic configuration of aninformation recording and reproducing apparatus according to theembodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a recording controlunit shown in FIG. 5.

FIG. 7A is a circuit diagram showing a configuration of an LD drivershown in FIG. 6, and FIG. 7B is a graph showing a characteristic of alaser diode.

FIGS. 8A to 8C are diagrams showing laser driving waveforms (recordingstrategies) according to the basic embodiment of the present invention.

FIGS. 9A to 9C are diagrams showing laser driving waveforms (recordingstrategies) according to the first modification of the presentinvention.

FIGS. 10A to 10C are diagrams showing laser driving waveforms (recordingstrategies) according to the second modification of the presentinvention.

FIGS. 11A to 11C are diagrams showing laser driving waveforms (recordingstrategies) according to the third modification of the presentinvention.

FIGS. 12A to 12C are diagrams showing laser driving waveforms (recordingstrategies) according to the fourth modification of the presentinvention.

FIG. 13 shows pulse widths of laser driving waveforms according to thefourth modification and setting examples of each power level.

FIGS. 14A to 14C are diagrams showing laser driving waveforms (recordingstrategies) according to the seventh modification of the presentinvention.

FIGS. 15A to 15C are diagrams showing laser driving waveforms (recordingstrategies) according to the eighth modification of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedbelow with reference to the attached drawings.

FIG. 1 shows an example of the strategy utilizing the multi-pulses whoseperiod is 1T. The example illustrates the strategy of the recording data8T and 3T. As shown in FIG. 1, the strategy is formed by a top pulse TP,a plurality of multi-pulses MP of 1T period and a cooling pulse CP. Thenumber of the multi-pulses MP is determined by a recording data length.In FIG. 1, the widths of the top pulse TP, the multi-pulse MP and thecooling pulse CP are respectively indicated as Ttop, Tmp and Tcl.

A level of the top pulse TP varies between a recording power level Prand an erasing power level Pe. A level of the multi-pulse MP variesbetween the recording power level Pr and a bias power level Pb. Thecooling pulse CP is equal to the bias power level Pb, and the bias powerlevel Pb is equal to the level which is increased by a predeterminedlevel from a zero level P0.

Since the multi-pulse whose period is 1T is utilized in this strategy,the optical disc cannot be heated and cooled for the time larger than 1Tin a multi-pulse interval.

A laser emitting waveform 60 at a bottom of FIG. 1 indicates a laseremitting waveform at the time of the high-speed recording at which thetime of 1T is smaller than 10 ns. When the time of 1T becomes smallerthan 10 ns, the recording pulse width sometimes becomes smaller than 5ns. For example, assuming that about 2 ns is respectively needed atrise-up and fall-down time periods of a laser light source, asillustrated in the waveform 60, the pulse waveform which is originallyalmost rectangular becomes rounded by a transient response, and thepulse waveform cannot keep rectangular shape. Therefore, pits cannot beaccurately formed on the disc due to the differences of thecharacteristics of the laser light source and a driving circuit betweenthe recording apparatuses.

Based on the above-mentioned examination, in the present invention, bysetting the pulse widths of each pulse forming the strategy to be largerthan 1T, it becomes possible that the pits are accurately formed even inthe high-speed recording. Basically, the laser driving waveform(strategy) corresponding to the recording mark length is formed by onetop pulse, necessary number of multi-pulses corresponding to therecording mark length, and one cooling pulse. Therefore, in a case of ashort recording mark, the laser driving waveform is formed by thecombination of one top pulse and one cooling pulse. In a case of a longrecording mark, the laser driving waveform is formed by one top pulse,the necessary number of the multi-pulses and one cooling pulse.

When the above-mentioned laser driving waveform is utilized, it isbasically needed that the widths of the top pulse and the multi-pulseare appropriately determined in order to correspond to the high-speedrecording. Therefore, in the present invention, the widths of the toppulse and the multi-pulse are determined as follows.

First of all, it is examined the recording marks of what length can beformed by the combination of one top pulse and one cooling pulse. FIG.2A is a graph which shows a relation between the width Tcl of thecooling pulse CP and the recording mark length when the top pulse widthTtop is increased to 1.0T, 1.5T, 2.0T, by prescribing the width Ttop ofthe top pulse TP as a parameter. It is noted that the recording marksare measured after repeating over-writing 10 times, under a conditionthat the recording power Pr=18 mW and an erasing power Pe=9 mW at therecording speed being corresponding to about 4-times speed of a DVD. Thewidth Tcl of the cooling pulse is varied until the marks cannot beaccurately recorded. Thus, since shapes of the recording marks aredistorted beyond a limit illustrated in the graph, and the marks cannotbe appropriately recorded, the cooling pulse width cannot be increasedfurther. The width Ttop of the top pulse TP and the width Tcl of thecooling pulse CP are prescribed as shown in FIG. 2B.

With reference to the graph in FIG. 2A, it is understood that longerrecording marks can be formed by increasing the top pulse width Ttop andthe cooling pulse width Tcl. However, no further effect is expected evenif the top pulse width Ttop is further increased to be larger thanTtop=2.0T. No matter how long the cooling pulse width Tcl is increasedwithin the limit at which the recording marks are not distorted, it isunderstood that only the recording marks of at most 5T can be formed.Namely, it is understood that the recording mark equal to or larger than6T cannot be formed by the combination of one top pulse TP and onecooling pulse CP.

Next, an appropriate period of the multi-pulse is examined. The numberof the multi-pulses in the laser driving waveform depends on therecording mark length. In order to examine that a signal can beaccurately recorded by the multi-pulse period of what length, therecording marks of 12T are recorded by prescribing the multi-pulseperiod as 3 kinds of periods, i.e., 2T, 3T and 4T periods, as shown inFIG. 3A. FIG. 3B is a graph which shows a relation between a pulse dutyand a signal modulating degree, as to the recording marks of the 3 kindsof the multi-pulse periods. Here, the pulse duty is a ratio of an H(High) level period and an L (Low) level period in the multi-pulseperiod. The signal modulating degree is a value which indicatesmagnitude of a reproducing signal of the formed recording marks, and thevalue of the signal modulating degree becomes large when the recordingmarks are formed in accurate shapes.

With reference to the graph in FIG. 3B, when the multi-pulse period is2T, it is understood that the signal modulating degree is maximum whenthe pulse duty is at about 0.4, while the signal modulating degreelowers comparatively largely when the pulse duty deviates from 0.4. Onthe other hand, when the multi-pulse period is 3T and 4T, the signalmodulating degree is larger than that in a case of 2T, and the signalmodulating degree comparatively indicates a flat characteristic againsta variation of the pulse duty. Therefore, in view of the signalmodulating degree, the multi-pulse period is preferred to be 3T or 4T,and there are few differences between the periods of 3T and 4T. However,it is generally recognized that the formed recording marks tend to bemore easily distorted when the number of the recording pulses is smallin the long mark recording, than those when the number of the recordingpulses is large. In this point, it is recognized that an optimummulti-pulse width is 3T.

According to the above-mentioned examination, it is found out asfollows: (1) the recording marks which are at least equal to or largerthan 6T mark should be formed by the combination of the top pulse, thenecessary number of the multi-pulses and the cooling pulse, and (2) itis preferred that the optimum multi-pulse width is 3T. As a result, itis understood that the preferred laser driving waveform (strategy) inthe high-speed recording are the waveform having the top pulse andcooling pulse of pulse widths corresponding to the recording mark lengthas to the recording marks 3T to 5T, and the waveform having the toppulse, the multi-pulses of 3T period whose number corresponds to therecording mark length and the cooling pulse as to the recording marksequal to or larger than 6T, as schematically shown in FIG. 4. In thisinvention, it is possible to accurately form the recording marks even atthe time of the high-speed recording, by utilizing such a strategy.

According to one aspect of the present invention, there is provided aninformation recording apparatus including a signal generating unit whichgenerates a light source driving signal having a top pulse andmulti-pulse of a necessary number corresponding to a recording marklength of recording data, and a recording unit which irradiates arecording light on an optical recording medium by driving a light sourcebased on the light driving signal and forms recording marks on theoptical recording medium, wherein the signal generating unit includes, amulti-pulse generating unit which generates a multi-pulse having aperiod 3-times larger than a base clock period T of the recording mark,and a top pulse generating unit which generates first identical-shapetop pulses when the recording mark length is 3nT (“n” is an integralnumber), and second identical-shape top pulses when the recording marklength is (3n+1)T, and third identical-shape top pulses when therecording mark length is (3n+2) T. According to the above informationrecording apparatus, since the period of the multi-pulse is 3-timeslarger than the base clock period T of the recording mark, the recordingcan be accurately executed at the time of the high-speed recording.

In the above-mentioned information recording apparatus, the light sourcedriving signal may include only the top pulse when the recording marklength is from 3T to 5T. The second top pulse width may be larger thanthe first top pulse width, and the third top pulse width may be largerthan the second top pulse width.

In one feature of the above information recording apparatus, the thirdtop pulse may be formed by two pulses. Thus, even when the recordingmarks cannot be preferably formed by one top pulse due to a recordingcharacteristic of the optical disc subjected to recording, the recordingmarks can be preferably formed by two pulses.

In another feature of the above information recording apparatus, bymaking a back edge position of the multi-pulse correspond to the baseclock position, back positions of the long recording marks are easy toalign, and the recording with less recording and reproducing jitter ispossible. Further, by making the cooling pulse portion width of the lastmulti-pulse included in the light source driving waveform correspondingto the recording marks equal to or larger than 6T constant, it ispossible that back positions of the long recording marks are much easierto align.

In the above information recording apparatus, preferably, the back edgesof two pulses forming the third top pulse may respectively correspond tothe positions of 3T and 5T from rise-up of the recording data. Also, thetop pulse width and the multi-pulse width may be equal to or larger than0.5T.

In the above information recording apparatus, a time from rise-up of therecording data to a rise-up of the top pulse may be constant,irrespective of the recording mark length. Thus, the head positions ofthe recording marks are easy to align, and the recording with lessrecording and reproducing jitter is possible.

Moreover, in the above information recording apparatus, by making thepower levels of the first to the third top pulses different from eachother, preferable recording adapted to the recording characteristic ofthe optical disc is possible by adjusting not only the pulse width butalso the recording power.

Next, the preferred embodiments of the present invention will bedescribed below with reference to the attached drawings.

[Configuration of Information Recording and Reproducing Apparatus]

FIG. 5 schematically shows the whole configuration of the informationrecording and reproducing apparatus according to the embodiment of thepresent invention. An information recording and reproducing apparatus 1records information on an optical disc D, and reproduces the informationfrom the optical disc D. As the optical disc D, for example, a CD-RW(Compact Disc-Rewritable) or a DVD-RW, which are capable of erasing andrecording the information a plurality of times, may be used.

The information recording and reproducing apparatus 1 includes anoptical pickup 2 which irradiates a recording beam and a reproducingbeam on the optical disc D, a spindle motor 3 which controls rotation ofthe optical disc D, a recording control unit 10 which controls therecording of the information on the optical disc D, a reproducingcontrol unit 20 which controls reproduction of the information alreadyrecorded on the optical disc D, a spindle servo which controls rotationof the spindle motor 3, and a servo control unit 30 which executesvarious kinds of servo control including a focus servo and a trackingservo, both of width are relative position control of the optical pickup2 to the optical disc D.

The recording control unit 10 receives the recording data and generatesa driving signal SD for driving a laser diode inside the optical pickup2 by a process described below, and supplies the signal SD to theoptical pickup 2.

The reproducing control unit 20 receives a read-out RF signal Srf whichis output from the optical pickup 2, and generates and outputsreproducing data by executing a predetermined demodulating process anddecoding process to the signal Srf.

The servo control unit 30 receives the read-out RF signal Srf from theoptical pickup 2, and, based on the signal, supplies a servo signal S1,such as a tracking error signal and a focus signal, to the opticalpickup 2, and also supplies a spindle servo signal S2 to the spindlemotor 3. Thus, various kinds of servo processes, such as a trackingservo, a focus servo and a spindle servo, are executed.

The present invention mainly relates to a method of the recording in therecording control unit 10, and various kinds of known methods can beapplied, as to the reproducing control and the servo control. Therefore,an explanation thereof is not given in detail here.

Though FIG. 5 illustrates the information recording and reproducingapparatus as an example of the embodiment of the present invention, itis also possible to apply the present invention to an informationrecording apparatus dedicated to recording.

FIG. 6 shows an internal configuration of the optical pickup 2 and therecording control unit 10. As shown in FIG. 6, the optical pickup 2includes a laser diode LD which generates the recording beam forrecording the information to the optical disc D and the reproducing beamfor reproducing the information from the optical disc D.

The optical pickup 2 additionally includes well-known components such asa light detector which receives a reflected beam by the optical disc Dof the reproducing beam and generates the read-out RF signal Srf, and anoptical system which guides the recording beam, the reproducing beam andthe reflected beam to appropriate directions. However, drawings anddetailed explanations thereof are omitted here.

On the other hand, the recording control unit 10 includes a laser diode(LD) driver 12 and a controller 15. The LD driver 12 supplies a currentcorresponding to the recording signal to the laser diode LD, and recordsthe information on the optical disc D.

FIG. 7A shows a detailed configuration of the LD driver 12. As shown inFIG. 7A, the LD driver 12 includes a current source 17 b for the biaspower level, a current source 17 e for the erasing power level, acurrent source 17 r for the recording power level, switches 18 b, 18 eand 18 r.

The current source 17 b for the bias power level generates the flow of adriving current Ib for driving the laser diode LD to emit the laserlight with the bias power Pb, and the driving current Ib is supplied tothe laser diode LD via the switch 18 b. Thus, when the switch 18 b isswitched on, the driving current Ib of the bias power is supplied to thelaser diode LD, and when the switch 18 b is switched off, the drivingcurrent Ib is not supplied.

The current source 17 e for the erasing power level generates the flowof the driving current I1 for driving the laser diode LD to emit thelaser light with the erasing Power Pe. The driving current I1 issupplied to the laser diode LD via the switch 18 e. The driving currentI1 is added to the driving current Ib of the bias power, and the drivingcurrent Ie of the erasing power is supplied to the laser diode LD viathe switch 18 e.

The current source 17 r for the recording power level generates the flowof the driving current I2 for driving the laser diode LD to emit thelaser light with the recording power Pr. The driving current I2 issupplied to the laser diode LD via the switch 18 r. The driving currentI2 is added to the driving current Ib of the bias power, and the drivingcurrent Ir of the recording power is supplied to the laser diode LD viathe switch 18 r.

Therefore, by controlling the ON/OFF of the switches 18 b, 18 e, and 18r, the laser diode LD serving as the laser light source can be drivenwith any one of the bias power Pb, the erasing power Pe or the recordingpower Pr.

FIG. 7B shows a relation between the driving current supplied to thelaser diode LD and an output power of the laser light emitted from thelaser diode LD. As understood in FIG. 7B, when the driving current Ib issupplied to the laser diode LD, the laser light is emitted by the biaspower Pb. Moreover, when the driving current I1 is added under thecondition, the laser light is emitted by the erasing power Pe. When thedriving current I2 is added instead of the driving current I1, the laserlight is emitted by the recording power Pr.

Embodiment of Strategy

Next, the description will be given of the embodiment of the strategyfor the high-speed recording according to the present invention.

Basic Embodiment

FIGS. 8A to 8C show the strategy according to a basic embodiment. Therecording marks to be recorded on the disc, corresponding to therecording data, are 3T to 11T and 14T, and FIGS. 8A to 8C show the laserdriving waveform corresponding to each recording mark length. In theembodiment of the present invention, the recording mark lengths 3T to11T and 14T are classified into three groups. Concretely, as shown inFIGS. 8A to 8C, the lengths are classified into a group G1 of therecording mark length=3nT, a group G2 of the recording marklength=(3n+1)T, and a group G3 of the recording mark length=(3n+2) T. Itis noted that “n” is a positive integral number from 1 to 4.

Namely, the recording mark lengths 3T, 6T and 9T belong to the group G1,and the laser driving waveforms thereof are illustrated in FIG. 8A. Therecording mark lengths 4T, 7T and 10T belong to the group G2, and thelaser driving waveforms thereof are illustrated in FIG. 8B. Therecording mark lengths 5T, 8T and 11T belong to the group G3, and thelaser driving waveforms thereof are illustrated in FIG. 8C. It is notedthat the base clocks (1T period) of the recording data are indicated atthe top of each drawing.

As explained above, the laser driving waveforms corresponding to therecording mark lengths 3T to 5T are formed by the combination of the toppulse TP and the cooling pulse CP, and no multi-pulses are included.Also, in the laser driving waveforms of the recording mark lengths 3T to5T, the top pulse width Ttop and the cooling pulse width Tcl aredetermined according to the recording mark lengths. Namely, the toppulse width Ttop and the cooling pulse width Tcl are shortest at 3T,middle at 4T and longest at 5T.

The laser driving waveforms of the recording mark lengths 6T to 8T arerespectively formed by the top pulse, the cooling pulse and onemulti-pulse. The laser driving waveforms of the recording mark lengths9T to 11T are respectively formed by the top pulse, the cooling pulse,and two multi-pulses. The laser driving waveform of the recording marklength 14T is formed by the top pulse, the cooling pulse and threemulti-pulses.

As understood in FIGS. 8A to 8C, as to the recording mark lengthbelonging to each group, the shapes of the top pulses are identical andregularly formed. Namely, the laser driving waveforms of the recordingmark lengths 3T, 6T and 9T belonging to the group G1 have theidentical-shape top pulses, and the laser driving waveforms of therecording mark lengths 4T, 7T and 10T belonging to the group G2 have theidentical-shape top pulses. The laser driving waveforms of the recordingmark lengths 5T, 8T, 11T and 14T belonging to the group G3 have theidentical-shape top pulses.

Further, all the laser driving waveforms of the recording mark lengthsequal to or larger than 6T, each including one or more multi-pulse havethe identical-shape multi-pulses whose periods are 3T. Theaforementioned conclusion that the optimum multi-pulse period is 3T isreflected in this point.

As explained above, in the embodiment, based on the above-mentionedexamined result, the laser driving waveforms of the recording marksequal to or smaller than 5T are formed by the combination of the toppulse and the cooling pulse, and the top pulse width and the coolingpulse width are determined according to the recording mark lengths. Thelaser driving waveforms of the recording marks equal to or larger than6T are formed by the top pulse, the multi-pulses whose numbercorresponds to the recording mark lengths, and the cooling pulse. Thus,it is possible to form pits of accurate shape at the time of thehigh-speed recording.

(1st Modification)

Next, the strategy according to the first modification will beexplained. FIGS. 9A to 9C show the laser driving waveform of eachrecording mark length according to the first modification. The firstmodification is different from the basic embodiment in that the toppulse TP is formed by the two pulses for the recording mark belonging tothe group G3. In the first modification, the laser driving waveforms ofthe recording mark lengths belonging to the groups G1 and G2 areidentical to those of the basic embodiment shown in FIGS. 8A to 8C.

As to the recording marks belonging to the group G3, i.e., 5T, 8T, 11Tand 14T, it is determined whether the top pulse TP is one, like thebasic embodiment shown in FIGS. 8A to 8C, or two, like the firstmodification, dependently on the recording characteristic of the opticaldisc subjected to the recording. Namely, the first modification iseffective when 5T mark can not be preferably formed by only a pair ofthe top pulse TP and the cooling pulse CP like the basic embodiment, orwhen distortion occurs to the marks 8T, 11T and 14T by only one toppulse TP.

(2nd Modification)

Next, the strategy according to the second modification will beexplained. FIGS. 10A to 10C show the laser driving waveform of eachrecording mark according to the second modification. As shown in FIGS.10A to 10C, the back edge of the multi-pulse train of the recording markequal to or larger than 6T corresponds to the base clock of 1T period inthe second modification. Because of this, since the back end positionsof the long recording marks are easy to align with each other, therecording with less recording and reproducing jitter is possible.

(3rd Modification)

Next, the strategy according to the third modification will beexplained. FIGS. 11A to 11C show the laser driving waveform of eachrecording mark according to the third modification. In the thirdmodification, in addition to the basic embodiment shown in FIGS. 8A to8C, first of all, identically to the second modification shown in FIGS.10A to 10C, the back edge of the multi-pulse train of the recording markequal to or larger than 6T corresponds to the base clock of 1T period,and further, the width of the cooling pulse portion of the lastmulti-pulse in the laser driving waveform of the recording mark equal toor larger than 6T is made identical. Namely, as shown in FIGS. 11A to11C, for all the recording marks equal to or larger than 6T, the widthof the cooling pulse portion of the last multi-pulse is set to “W”.

According to the third embodiment, while the position of the shortrecording mark which is formed by the combination of the top pulse andthe cooling pulse is kept adjustable, the back positions of the longrecording marks are easier to align than that in the secondmodification, and the preferable recording with less recording andreproducing jitter is possible.

(4th Modification)

Next, the strategy according to the fourth modification will beexplained. FIGS. 12A to 12C show the laser driving waveform of eachrecording mark according to the fourth modification. In the fourthmodification, first of all, identically to the first modification shownin FIGS. 9A to 9C, the top pulses of the recording marks 5T, 8T, 11T and14T belonging to the group G3 are respectively formed by two pulses. Theback edges of two top pulses of the laser driving waveform of therecording mark belonging to the group G3 are respectively adjusted tothe positions of 3T and 5T from the rise-up of the recording data.Moreover, identically to the third modification, the back edge of themulti-pulse train of the recording mark equal to or larger than 6Tcorresponds to the base clock of 1T, and the width of the cooling pulseportion of the last multi-pulse in the laser driving waveform of therecording mark equal to or larger than 5T is made identical (“W”).

According to the fourth modification, while the positions of therecording marks 3T and 4T which are formed by the combination of the toppulse and the cooling pulse are kept adjustable, the back position ofthe long recording mark is much easier to align than the secondmodification, and the preferable recording with less recording andreproducing jitter is possible.

A table in FIG. 13 shows an example of each value in the laser drivingwaveform in the fourth modification. FIG. 13 shows two examples of therecording speed corresponding to 4-times higher speed of the DVD. It isnoted that sign of 3nTdtop and (3n+1) Tdtop is indicated as positivewhen the back edge of the top pulse is ahead of the base clock (i.e., itshifts to the left side), and the sign is indicated as negative when theback edge of the top pulse is behind of the base clock (i.e., it shiftsto the right side).

(5th Modification)

Next, the fifth modification will be explained. The fifth modificationis a case that the pulse widths of the top pulse TP and multi-pulse MPof the basic embodiment shown in FIGS. 8A to 8C are limited. Concretely,they are determined as follows,

-   -   Top pulse width of group G1: 0.5T≦3nTtop≦3T    -   Top pulse width of group G2: 0.5T≦(3n+1)Ttop≦3T    -   Top pulse width of group G3: 0.5T≦(3n+2)Ttop≦3T    -   Multi-pulse width of each group: 0.5T≦Tmp≦2.5T.

As explained above, for example, 1T is equal to about 10 ns, and 0.5T isequal to about 5 ns in 4-times higher speed recording of the DVD. Sincethe pulse width smaller than 5 ns is too narrow as shown in FIG. 1, therecording marks cannot be accurately formed. That is why each top pulsewidth and multi-pulse width is determined to be larger than 0.5T. Inaddition, since an L-level period of the multi-pulse becomes equal to orsmaller than 0.5T if the multi-pulse width is equal to or larger than2.5T, the multi-pulse width is determined to be smaller than 2.5T.

Like this, by limiting the pulse width in each portion of the laserdriving waveform, it is possible that the recording is executed in anarea in which an accurate laser emitting waveform is obtained.

(6th Modification)

Next, the sixth modification will be explained. The sixth modificationis a case that the pulse widths of the top pulse TP and the multi-pulseMP in the first modification shown in FIGS. 9A to 9C are limited.Concretely, they are determined as follows,

-   -   Top pulse width of group G1: 0.5T≦3nTtop≦3T    -   Top pulse width of group G2: 0.5T≦(3n+1)Ttop≦3T    -   First top pulse width of group G3: 0.5T≦(3n+2)Ttop1≦2T    -   Second top pulse width of group G3: 0.5T≦(3n+2)Ttop2≦1.5T    -   Multi-pulse width of each group: 0.5T≦Tmp≦2.5T.

Here, the reason why each top pulse width and multi-pulse width isdetermined to be equal to or larger than 0.5T is identical to the reasonwhich is mentioned in the fifth modification. As understood in FIGS. 7Aand 7B, since the top pulse in the group G3 is formed by two pulses inthe first modification, a range of the pulse width is set for eachpulse. Thus, by limiting the pulse width in each portion of the laserdriving waveform, it is possible that the recording is executed in thearea in which the accurate laser emitting waveform is obtained in thesixth modification, too.

(7th Modification)

Next, the seventh modification will be explained. The seventhmodification is a case that a time Td from the rise-up of the recordingdata to the rise-up of the top pulse is set to be constant, irrespectiveof the recording mark length, in the above-mentioned basic embodimentand the first to sixth modifications. As an example, FIGS. 14A to 14Cshow the laser recording waveforms of a case that the seventhmodification is applied to the fourth modification shown in FIGS. 12A to12C. As shown in FIGS. 14A to 14C, irrespective of the recording marklength, the time Td from the rise-up of the recording data to therise-up of the top pulse is constant in all the laser recordingwaveforms. Thus, since the rise-up positions of the top pulses arealigned in all the recording marks in the seventh modification, the headposition of each recording mark is easy to align with each other, andthe preferable recording with less recording and reproducing jitters ispossible.

(8th Modification)

Next, the eighth modification will be explained. The eighth modificationis a case that the recording power level of each top pulse portion inthree groups G1 to G3 are set to be different from each other for theabove-mentioned basic embodiment and the first to seventh modifications.FIGS. 15A to 15C show the laser driving waveforms of a case that theeighth modification is applied to the basic modification shown in FIGS.8A to 8C. As understood in FIGS. 15A to 15C, the recording power levelof the top pulse in each group G1 to G3 is3nTPw≦(3n+1)TPw≦(3n+2)TPw,if it is defined that the recording power level of the top pulse in thegroup G1 is “3nTPw”, the recording power level of the top pulse in thegroup G2 is “(3n+1)TPw”, and the recording power level of the top pulsein the group G3 is “(3n+2)TPw”.

Thus, in the eighth modification, by adjusting the recording power toadapt to the recording characteristic of the optical disc subjected tothe recording in addition to the pulse width, the preferable recordingadapted to the recording characteristic of the optical disc is possible.

Though examples shown in FIGS. 15A to 15C indicate examples that therecording power levels becomes larger in the order of the groups G1 toG3, an application of the eighth embodiment is not limited to this.Namely, the recording power level can be suitably determined accordingto the pulse width of each portion in the laser driving waveform of eachgroup.

INDUSTRIAL APPLICABILITY

The information recording apparatus and the information recording methodaccording to this invention can be used at the time of recording theinformation onto the optical disc by using the laser light and the like.

1. An information recording apparatus comprising: a signal generatingunit which generates a light source driving signal having a top pulseand multi-pulse of a necessary number corresponding to a recording marklength of recording data; and a recording unit which irradiates arecording light on an optical recording medium by driving a light sourcebased on the light driving signal and forms recording marks on theoptical recording medium, wherein the signal generating unit includes: amulti-pulse generating unit which generates a multi-pulse includingplural pulses each having a period 3-times larger than a base clockperiod T of the recording mark; and a top pulse generating unit whichgenerates first identical-shape top pulses for recording marks whenrecording 3nT mark length, and second identical-shape top pulses forrecording marks, when recording at (3n+1)T mark length, and thirdidentical-shape top pulses for recording marks when recording at (3n+2)Tmark length wherein the third pulse is a multi-pulse formed by twopulses and n is a positive number from 1-4.
 2. The information recordingapparatus according to claim 1, wherein the light source driving signalincludes only the top pulse when the recording mark length is 3T to 5T.3. The information recording apparatus according to claim 1, wherein awidth of the second top pulse is larger than a width of the first toppulse, and wherein a width of the third top pulse is larger than a widthof the second top pulse.
 4. The information recording apparatusaccording to claim 1, wherein a back edge position of the multi-pulsecorresponds to a position of the base clock.
 5. The informationrecording apparatus according to claim 1, wherein the multi-pulseincludes a cooling pulse portion, and wherein widths of the coolingpulse portions of last multi-pulses included in a light source drivingwaveform corresponding to a recording mark larger than 6T are identical.6. The information recording apparatus according to claim 1, wherein theback edges of two pulses forming the third top pulse respectivelycorrespond to positions of 3T and 5T from rise-up of the recording data.7. The information recording apparatus according to claim 1, whereinwidths of the top pulse and the multi-pulse are equal to or larger than0.5T.
 8. The information recording apparatus according to claim 1,wherein a time from a rise-up of the recording data to a rise-up of thetop pulse is constant irrespective of the recording mark length.
 9. Theinformation recording apparatus according to claim 1, wherein powerlevels of the first to third top pulses are different from each other.10. An information recording method comprising: a signal generatingprocess which generates a light source driving signal having a top pulseand multi-pulse of a necessary number corresponding to a recording marklength of recording data; and a recording process which irradiates arecording light on an optical recording medium by driving a light sourcebased on the light driving signal, and forms recording marks on theoptical recording medium, wherein the signal generating processincluding: a multi-pulse generating process which generates amulti-pulse including plural pulses each having a period 3-times largerthan a base clock period T of the recording mark; and a top pulsegenerating unit which generates first identical-shape top pulses forrecording marks when recording 3nT mark length, and secondidentical-shape top pulses for recording marks, when recording at(3n+1)T mark length, and third identical-shape top pulses for recordingmarks when recording at (3n+2)T mark length, wherein the third pulse isa multi-pulse formed by two pulses and n is a positive number from 1-4.11. The information recording apparatus according to claim 1, whereinthe third top pulse is formed by two separate pulses.
 12. Theinformation recording method according to claim 10, wherein the thirdtop pulse is formed by two separate pulses.
 13. The informationrecording apparatus according to claim 1, wherein the third top pulsecomprises a first portion having a first level, a second portionfollowing the first portion and having a second level lower than thefirst level and a third portion following the second portion and havingthe first level.
 14. The information recording method according to claim10, wherein the third top pulse comprises a first portion having a firstlevel, a second portion following the first portion and having a secondlevel lower than the first level and a third portion following thesecond portion and having the first level.